Valtteri Bottas kept Mercedes on top of the timesheets as he amassed 143 laps on the second and final day of the Formula 1 in-season test at Bahrain.

Sebastian Vettel finished second fastest despite a frustrating day for Ferrari, with Scuderia Toro Rosso’s Carlos Sainz third.

Bottas ran without the T-wing for the first time since early in pre-season testing as he concentrated on tyre life.

After stopping on track before lunchtime, the Finn set a faster time than team-mate Lewis Hamilton’s Day 1 effort in the relative cool of the late afternoon.

“Today was very good. We got so much running done,” said Bottas.

“We were focusing all-day on the long-run pace, which was a bit of a problem for us on Sunday compared to Ferrari.”

Vettel managed only eight laps during morning running due to hydraulic issues, before losing more time in the afternoon as a garage blackout took down telemetry.

The German rallied thereafter to go second fastest, having finished Day 1 ninth while working on tyre development for Pirelli.

Sainz joined the pair in the 1:31s bracket after team-mate Daniil Kvyat took the morning session for STR.

McLaren had reason to be upbeat as Stoffel Vandoorne put 81 laps on the board after crippling engine problems for the Honda-powered team on Day 1.

“Today has probably been our best day this season so far,” said the Belgian as he finished fourth fastest.

“It’s the first time that we’ve had a day without any big problems, where we could actually get on with our programme.”

Kevin Magnussen was fifth as Haas F1 continued to work on its brake package.

Super Formula driver Pierre Gasly rounded out the top 10 for Red Bull Racing.

The Formula 1 World Championship continues with the Russian Grand Prix from April 28-30.

Result: Formula 1 in-season test Bahrain Day 2